Add a helper dealing with handling the syncing of a buffered write fallback
for direct I/O.
Signed-off-by: Christoph Hellwig <[email protected]>
---
fs/libfs.c | 36 +++++++++++++++++++++++++
include/linux/fs.h | 2 ++
mm/filemap.c | 66 +++++++++++-----------------------------------
3 files changed, 53 insertions(+), 51 deletions(-)
diff --git a/fs/libfs.c b/fs/libfs.c
index 89cf614a327158..ad37a49e2ecfb7 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1613,3 +1613,39 @@ u64 inode_query_iversion(struct inode *inode)
return cur >> I_VERSION_QUERIED_SHIFT;
}
EXPORT_SYMBOL(inode_query_iversion);
+
+ssize_t direct_write_fallback(struct kiocb *iocb, struct iov_iter *iter,
+ ssize_t direct_written, ssize_t buffered_written)
+{
+ struct address_space *mapping = iocb->ki_filp->f_mapping;
+ loff_t pos = iocb->ki_pos - buffered_written;
+ loff_t end = iocb->ki_pos - 1;
+ int err;
+
+ /*
+ * If the buffered write fallback returned an error, we want to return
+ * the number of bytes which were written by direct I/O, or the error
+ * code if that was zero.
+ *
+ * Note that this differs from normal direct-io semantics, which will
+ * return -EFOO even if some bytes were written.
+ */
+ if (unlikely(buffered_written < 0))
+ return buffered_written;
+
+ /*
+ * We need to ensure that the page cache pages are written to disk and
+ * invalidated to preserve the expected O_DIRECT semantics.
+ */
+ err = filemap_write_and_wait_range(mapping, pos, end);
+ if (err < 0) {
+ /*
+ * We don't know how much we wrote, so just return the number of
+ * bytes which were direct-written
+ */
+ return err;
+ }
+ invalidate_mapping_pages(mapping, pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
+ return direct_written + buffered_written;
+}
+EXPORT_SYMBOL_GPL(direct_write_fallback);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e4efc1792a877a..576a945db178ef 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2738,6 +2738,8 @@ extern ssize_t __generic_file_write_iter(struct kiocb *, struct iov_iter *);
extern ssize_t generic_file_write_iter(struct kiocb *, struct iov_iter *);
extern ssize_t generic_file_direct_write(struct kiocb *, struct iov_iter *);
ssize_t generic_perform_write(struct kiocb *, struct iov_iter *);
+ssize_t direct_write_fallback(struct kiocb *iocb, struct iov_iter *iter,
+ ssize_t direct_written, ssize_t buffered_written);
ssize_t vfs_iter_read(struct file *file, struct iov_iter *iter, loff_t *ppos,
rwf_t flags);
diff --git a/mm/filemap.c b/mm/filemap.c
index ddb6f8aa86d6ca..137508da5525b6 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -4006,23 +4006,19 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
struct file *file = iocb->ki_filp;
struct address_space *mapping = file->f_mapping;
- struct inode *inode = mapping->host;
- ssize_t written = 0;
- ssize_t err;
- ssize_t status;
+ struct inode *inode = mapping->host;
+ ssize_t ret;
- err = file_remove_privs(file);
- if (err)
- goto out;
+ ret = file_remove_privs(file);
+ if (ret)
+ return ret;
- err = file_update_time(file);
- if (err)
- goto out;
+ ret = file_update_time(file);
+ if (ret)
+ return ret;
if (iocb->ki_flags & IOCB_DIRECT) {
- loff_t pos, endbyte;
-
- written = generic_file_direct_write(iocb, from);
+ ret = generic_file_direct_write(iocb, from);
/*
* If the write stopped short of completing, fall back to
* buffered writes. Some filesystems do this for writes to
@@ -4030,45 +4026,13 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
* not succeed (even if it did, DAX does not handle dirty
* page-cache pages correctly).
*/
- if (written < 0 || !iov_iter_count(from) || IS_DAX(inode))
- goto out;
-
- pos = iocb->ki_pos;
- status = generic_perform_write(iocb, from);
- /*
- * If generic_perform_write() returned a synchronous error
- * then we want to return the number of bytes which were
- * direct-written, or the error code if that was zero. Note
- * that this differs from normal direct-io semantics, which
- * will return -EFOO even if some bytes were written.
- */
- if (unlikely(status < 0)) {
- err = status;
- goto out;
- }
- /*
- * We need to ensure that the page cache pages are written to
- * disk and invalidated to preserve the expected O_DIRECT
- * semantics.
- */
- endbyte = pos + status - 1;
- err = filemap_write_and_wait_range(mapping, pos, endbyte);
- if (err == 0) {
- written += status;
- invalidate_mapping_pages(mapping,
- pos >> PAGE_SHIFT,
- endbyte >> PAGE_SHIFT);
- } else {
- /*
- * We don't know how much we wrote, so just return
- * the number of bytes which were direct-written
- */
- }
- } else {
- written = generic_perform_write(iocb, from);
+ if (ret < 0 || !iov_iter_count(from) || IS_DAX(inode))
+ return ret;
+ return direct_write_fallback(iocb, from, ret,
+ generic_perform_write(iocb, from));
}
-out:
- return written ? written : err;
+
+ return generic_perform_write(iocb, from);
}
EXPORT_SYMBOL(__generic_file_write_iter);
--
2.39.2
On Wed, May 24, 2023 at 09:00:36AM +0200, Miklos Szeredi wrote:
> > +ssize_t direct_write_fallback(struct kiocb *iocb, struct iov_iter *iter,
> > + ssize_t direct_written, ssize_t buffered_written)
> > +{
> > + struct address_space *mapping = iocb->ki_filp->f_mapping;
> > + loff_t pos = iocb->ki_pos - buffered_written;
> > + loff_t end = iocb->ki_pos - 1;
> > + int err;
> > +
> > + /*
> > + * If the buffered write fallback returned an error, we want to return
> > + * the number of bytes which were written by direct I/O, or the error
> > + * code if that was zero.
> > + *
> > + * Note that this differs from normal direct-io semantics, which will
> > + * return -EFOO even if some bytes were written.
> > + */
> > + if (unlikely(buffered_written < 0))
> > + return buffered_written;
>
> Comment/code mismatch. The comment says:
>
> if (buffered_written < 0)
> return direct_written ?: buffered_written;
Yeah. And the old code matches the comment, so I'll update to that.
I'm really wondering how I could come up with a good test case for
this..
On 5/24/23 08:38, Christoph Hellwig wrote:
> Add a helper dealing with handling the syncing of a buffered write fallback
> for direct I/O.
>
> Signed-off-by: Christoph Hellwig <[email protected]>
> ---
> fs/libfs.c | 36 +++++++++++++++++++++++++
> include/linux/fs.h | 2 ++
> mm/filemap.c | 66 +++++++++++-----------------------------------
> 3 files changed, 53 insertions(+), 51 deletions(-)
>
Reviewed-by: Hannes Reinecke <[email protected]>
Cheers,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
[email protected] +49 911 74053 688
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